The invention relates to a method and apparatus for folding/unfolding the blades of a rotary-wing aircraft rotor, such as a helicopter main rotor. More particularly but not exclusively, the invention relates to a method and apparatus which may be advantageously used to assist in manually folding the blades of a helicopter main rotor towards the rear, substantially along the fuselage and tail boom of the helicopter, in order to reduce the space required, during periods when it is out of service and/or in order to make it easier to stow in a hangar, especially on a ship, or to load and stow in the hold of a transport aircraft.
In the flight configuration, rotary wing aircraft blades are connected to the rotor hub by connecting means which lock the blades in this unfolded position, in which their freedom of movement in a plane substantially perpendicular to the axis of rotation of the rotor, or the plane of the rotor disc, is very limited due to the stiffness of the means retaining the blades and hinging them to the hub being added to the stiffness of the blade drag dampers, in the case of hinged rotors, or due to the stiffness of the flexible torsion arms of the hub to which the blades are connected on rotors of the semi-rigid type.
To fold a blade, it is therefore necessary firstly to unlock it in order to allow it to have large-amplitude swing-type movement, generally towards the rear, and then to lock it in the folded position to avoid unwanted unfolding or deployment movements. To unfold or deploy a blade, i.e. to return it to the flight configuration, the sequence of operations mentioned above is carried out in reverse order, i.e. the blade in the folded position is unlocked to allow it to have large-amplitude swing-type movement, generally towards the front, and is then locked in the unfolded position or flight configuration.
These operations must be carried out in compliance with strict procedures, in order that the folding/unfolding of the blades is carried out without damaging the blades or other parts of the helicopter, and without danger to any personnel who may be present, such as operators assisting in the folding/unfolding manoeuvres.
Rotary-wing aircraft with folding/unfolding rotor blades and in particular such main rotors of helicopters, typically have at least two blades, each of which is connected to the rotor hub and locked in the unfolded position in the flight configuration by means connecting the blade to the hub comprising, as is generally the case on state-of-the-art rotors, a connecting device forming a pivot axis and at least one other device the movement of which causes the blade to be unlocked, allowing it to be folded by pivoting about said pivot axis, preferably towards the rear, substantially along the fuselage and the tail boom of the rotary-wing aircraft.
To fold the blades, two main types of folding procedures and devices are currently employed, namely manual folding, involving one or more operators, and automatic folding.
As illustrated in FIG. 2, which shows the folding of a blade of the four-bladed main rotor 2 of the helicopter 1 in FIGS. 1, 3 and 4, by pivoting this blade relative to the hub 3 of the rotor 2, it is frequently the case that the means connecting the blade to the hub comprise two pins such as 9 substantially parallel with each other, and symmetrical either side of a longitudinal axis Xxe2x80x94X of the blade, to retain the blade root 8 in an outer radial yoke 11 of a substantially radial connecting device 10, relative to the axis of rotation of the rotor, and generally termed a cuff, itself connected to the hub 3 of the rotor 2 by retaining and hinging means (not described or shown, as they do not form part of the invention). One of the two pins 9 is removable (it is shown withdrawn in FIG. 2) to allow the blade to fold by pivoting its root 8 about the other pin 9 which thus constitutes the pivot or folding axis, as also shown in FIGS. 2 and 5 of U.S. Pat. No. 4,268,222 for respectively three-bladed and four-bladed rotors with star-shaped hubs with flexible arms.
Conventionally, manual folding takes place after preparation of the helicopter and its main rotor, this preparation consisting in chocking the helicopter by means of chocks and/or a parking brake, lining up the rotor to position the blades favourably, half of them being on the left and the other half on the right of the helicopter, substantially symmetrically relative to the longitudinal axis of the helicopter running from the rear forwards, (a blade being substantially aligned with the tail boom of the helicopter when the number of blades of the rotor is odd), locking the rotor in this position by means of a rotor brake or any other equivalent means, positioning the angle of attack of the blades at a fixed pitch value or within a certain pitch range and, where appropriate, locking the blades in pitch, so that the blades can be moved by pivoting without interference with each other or with other elements of the helicopter, then folding in succession all the blades of the rotor other than the one, if any, aligned with the tail boom, beginning on each side by folding the rearmost blade (when folding is towards the rear), and continuing on each side by folding the remaining blade, in the case of a rotor with four or five blades, or the rearmost of the remaining blades in the case of a rotor with at least six blades.
As is known and shown in FIGS. 1 to 5, for each of the blades 4 to 7, and where the means connecting each blade 4 to 7 to the hub 3 comprise, as described above and shown in FIG. 2, two blade pins 9, one of which is removable, the folding procedure consists, where folding is towards the rear, in 20 withdrawing the removable pin 9 situated furthest forward in order to unlock the blade 4 to 7 in its flight configuration, and in such a way that the blade 4 to 7 can pivot towards the rear about the one of the two pins 9 which is situated furthest to the rear, moving the blade 4 to 7 in rotation by means of a folding pole 12 equipped at its upper end with a hinged hook 13 to grip the blade close to its tip, and which is held and raised at its lower end by one or more operators 14, in order to support the blade 4 to 7, and counteract bending of the blade under the effect of its own weight, which tends to prevent the insertion or extraction of the removable pin 9 and, after rotation about the pivot pin 9 and when the blade has reached its folded position (as have the front left blade 4 and rear left blade 5 in FIG. 1) along the tail boom 15 of the helicopter 1, securing it to the rear structure of the fuselage 16 or the tail boom 15, and locking it in the folded position by means of this same folding pole 12 which is hooked on by the operator or operators 14 to supports 17 integrated in said structure (16-15), the folding pole 12 being held by straps 18 fastened to said structure (16-15).
Where appropriate, as described for example in U.S. Pat. No. 4,268,222, other tools to assist in folding may be used in addition to the folding poles, pole supports and straps, for example a support secured removably to the central parts of the hub, this support supporting the inner radial ends of rigid arms, the outer radial ends of which are connected removably to the upper end of the pivot pin of each blade or a service tool pin replacing said pivot pin, in order to limit the bending of the flexible arms of the star-shaped hub.
To facilitate the extraction and insertion of the removable blade pins, in order to facilitate the folding and unfolding of such blades, it is also known practice to use, as means of connecting the blade to the hub, expanding blade pins such as described in particular in patent U.S. Pat. No. 3,192,820, which are pins which in service run through bushes permanently installed in the blade roots and in the locked position have a diameter greater than their diameter in the unlocked position, due to the fact that they are locked by pivoting a pin lever which compresses, along the axis of the pin a stack of spring washers for example of the conical washer type, the axial compression of which causes radial expansion deforming the tubular pin which swells and is then locked in the corresponding bush of the blade root.
In the case of a four-bladed rotor (see FIGS. 1 to 5), manual folding of the four blades in succession is generally carried out in the following order: rear left blade 5, then front left blade 4, then rear right blade 7 and finally front right blade 6.
This manual folding procedure has a major disadvantage resulting from the fact that each of its steps requires the intervention of one or more operators 14, not only to withdraw the removable blade pins 9 but also and above all to support, hold and move the blades 4 to 7 by means of the folding poles 12, so that any failure by an operator 14 may lead to a loss of control of the movement of a blade. This may result in serious damage to the blades 4 to 7 and/or to the other components of the helicopter 1, as well as injuries to the operators 14. The risk is particularly great when folding is carried out in high winds, ashore or at sea, in the case of a helicopter on board ship, because of the sudden loads caused by the gusts of wind on the blades. This risk is greater still on a ship in heavy seas, since the operators are subjected to the rolling and/or pitching movements of the ship, on a deck which may be made slippery by the rain and/or the spray, etc. Operational conditions combining high winds and a rough sea make it impossible to execute rotor blade folding or unfolding operations in acceptable safety conditions. Operationally, manual folding is therefore confined to helicopters of low or medium tonnage, the blades of which have a weight which can still be controlled by the operators.
In other words, manual folding remains economical, as it can be effected using simple tools, but its operational performance and level of safety are limited.
Automatic folding procedures and devices, an example of which is described in EP 0 057 053, employ an automated sequence of operations executed by means constantly present on the rotor. In general, on an automatic folding rotor of this type, each blade has its root retained in a yoke of a folding fitting mounted so as to pivot about a folding axis at the outer radial end of a cuff connecting it to the hub, and this cuff supports at least one operating actuator, causing and controlling the pivoting of the corresponding blade and its folding fitting about its folding axis, and at least one locking actuator, causing locking or unlocking, at least in the flight configuration, on the cuff.
This type of automatic folding procedure and device can provide folding and unfolding in difficult conditions, but has major disadvantages because of the very high development and acquisition costs, so that automatic folding can only be envisaged for medium or large tonnage helicopters and, in addition, automatic folding has to be taken into account from the design stage of the rotor, and in particular of its hub, so that the installation of an automatic folding device on an existing helicopter initially lacking such a device involves complete redesign of at least the hub.
In other words, automatic folding offers an excellent level of operational and safety performance in all weathers, but its cost is extremely high, and it requires particularly stringent maintenance. This applies even more when the automatic folding device has to provide locking not only in pitch but also in drag and/or flapping of components of the hub, such as the cuffs connecting the blades to the hub.
The problem addressed by the invention is to propose a method and apparatus for folding/unfolding the blades which ensures that the folding/unfolding operations proceed satisfactorily on helicopters operating in difficult conditions, as is the case for example with helicopters on board ship, which may be subjected to particularly difficult wind and sea conditions.
Another aim of the invention is to propose a procedure and a device for folding/unfolding blades which are advantageously employed as a procedure and a device to assist manual folding/unfolding of rotor blades of the known type presented above, requiring the intervention of operators using folding poles to support the blades and facilitate withdrawal of the removable blade pins, and to move the blades in rotation and then lock them in the folded position by securing the poles to the rear structure of the helicopter.
According to a first aspect of the present invention, there is provided a method of folding/unfolding at least one blade of a multi-bladed rotor of a rotary-wing aircraft, with at least a first blade being connected to a hub of the rotor by a coupling comprising a pivotal connection defining a pivot axis and a releasable connection, release of which allows its blade to be pivoted about its pivot axis between an unfolded position and a folded position, the method comprising steps:
(a) removably attaching at least one variable-length linear actuator to the first blade and a second blade, each locked in a fixed position with respect to the hub which is itself locked stationary;
(b) releasing the first blade from its fixed position with respect to the hub;
(c) actuating the linear actuator to vary its length and bear against the second blade, thereby pivoting the first blade about its pivot axis to a new position with respect to the hub; and
(d) locking the first blade in the new position.
Folding or unfolding of any other blade to be folded or unfolded may be performed conventionally or preferably by attaching said linear actuator or other similar actuator to two blades, at least one of which is to be folded or unfolded, and by employing the procedure above, step by step, until the last blade of the rotor is folded or unfolded. The procedure according to the invention can therefore be employed with a single actuator, whatever the number of blades, provided that the actuator is moved to different positions on the rotor in the course of the folding or unfolding operation.
This procedure according to the invention can assist and even replace the action of the operators employing a conventional manual folding/unfolding procedure, by means of at least one simple removable actuator, which may economically be a simple double-acting linear jack, to provide the energy required for pivoting the blades, and to control this pivoting, so that although folding poles, which may be identical to those used at present, are attached to the blade tips and handled by operators on the ground, the only function of these poles, after the removable blade pins are extracted, is to prevent unwanted vertical movements due to gusts of wind on the blades, since the folding or unfolding manoeuvre properly so-called is performed by the removable linear actuator, whereas in conventional manual folding, these poles are also used to move or hold blades in rotation to fold or unfold them.
In one embodiment, where the second blade is coupled to the hub of the rotor in an analogous way to the first blade, the method further comprises after step (d) steps:
(e) releasing the second blade from its fixed position with respect to the rotor;
(f) actuating the linear actuator to vary its length and bear against the first blade, thereby pivoting the second blade about its pivot axis to a new position with respect to the hub; and
(g) locking the second blade in its new position.
This procedure, combining the action of at least one removable linear actuator with suitable steps of locking and unlocking the blades, enables said removable linear actuator, or each of them, to manoeuvre a first, unlocked blade, by bearing against the second, locked blade, and then to manoeuvre the second, unlocked blade, by bearing against the first, locked blade, which minimises the number of linear actuators required and the number of times they are operated, a single actuator being sufficient whatever the number of blades, if it is moved to different positions on the rotor, in the course of the folding or unfolding operation.
Also advantageously, before step (f) the method may further comprise removably attaching a link rod to the first blade locked in its new position and to a third blade whose position is fixed with respect to the hub, whereby under subsequent actuation the linear actuator bears against the first and third blades together when the second blade pivots about its axis. A link rod of this type, in particular when it is attached to two locked blades folded towards the rear, because of its stiffness strengthens the assembly comprising these two folded rear blades, the hub of the rotor and the rear part of the fuselage, to which the two folded blades are connected by being locked in this position. However, this rod is not essential if the dimensioning of this assembly is compatible with the forces encountered during the complete folding procedure and during the period of immobilisation, in particular to enable it to withstand gusts of wind.
For implementation of the method aspect of the invention as presented above, there is also proposed apparatus for folding/unfolding at least one blade of a multi-bladed rotor of a rotary-wing aircraft, with at least a first blade being connected to a hub of the rotor by a coupling comprising a pivotal connection defining a pivot axis and a releasable connection, release of which allows its blade to be pivoted about its pivot axis between an unfolded position and folded position, the apparatus comprising:
at least one variable length, removable linear actuator configured to be removably attached to two adjacent blades of the rotor and to exert forces in either direction along its longitudinal axis on two blades connected by the linear actuator; and
connectors for removably attaching the linear actuator to two adjacent blades, each connector comprising an end fitting integral with the linear actuator and an attachment device configured for attachment to one blade, the end fitting and the attachment device being releasably interconnectable.
For rotors with at least three blades, it is sufficient for the folding/unfolding apparatus to comprise a single actuator, but preferably two linear actuators, preferably substantially identical, each fitted at each of its two longitudinal ends with an end fitting for attaching removably to at least one attachment device fitted to a blade, so as not to have to carry out too great a number of operations successively fitting and removing a single actuator to fold or unfold all the blades.
Advantageously, the device comprises in addition at least one substantially rectilinear removable link rod, designed to be removably attached to two blades, in particular two blades locked in the folded position towards the rear, said rod being fitted for this purpose and at each of its two longitudinal ends with means for connecting it removably to one respectively of the blades.
The folding/unfolding method and apparatus aspects of the invention have the advantages that, because at least one removable linear actuator is used, movement of the blades is caused and controlled, thus avoiding any undesirable movement of a blade which might have broken free from the operators, so that for a reasonable cost of such a device, the blades can be folded safely in strong winds and/or heavy seas. The procedure and device according to the invention thus fill the gap which currently exists between the procedures and devices for manual folding, of low cost but with limited performance and safety, and automatic folding procedures and devices, offering good performance and good safety, but at very high cost.
Compared with an automatic folding device, the rotary-wing aircraft rotor of which the blades are to be folded does not permanently carry the folding/unfolding device of the invention, which is fitted to the rotor only when the rotary-wing aircraft is on the ground, at least during the blade folding/unfolding operations and, where appropriate, during the period of immobilisation of the folded blades. The saving in weight and therefore improvement in performance is very appreciable, since for a helicopter of the eight to ten tonne class, the weight saved is of the order of 100 kg.
In addition, as the folding/unfolding apparatus is only a tool used solely on rotary-wing aircraft on the ground, this tool is not subject to the same rules and constraints as equipment used in flight. The result is that development, acquisition and maintenance costs are markedly lower than those of a device carried on board the aircraft.
The invention may be applied to all types of existing helicopter rotors, whatever the number of blades, provided that the blades are able to pivot, substantially in the plane of the rotor disc, about one of the means connecting them to the hub (pin, bolt or other equivalent means). Adaptation of the invention to an existing helicopter requires no modification of the hub, in particular of the main rotor, and only the blades have to be equipped with means for removably attaching the linear actuator or actuators, and these attachment means may be at least partially integrated into the blades or completely removable from the latter.
For a new helicopter or more simply a new rotor, in particular a main rotor, for which blade folding is required, the folding/unfolding method and apparatus aspects of the invention do not add design constraints with regard to folding, so that the prime function of the hub, which is to control the lift of the rotor, can be optimised.
Depending on the number of blades of the rotor, the core method and apparatus defined above must be adapted to each rotor, but the same basic principle still applies, using at least one linear actuator attached to two adjacent blades of the rotor and bearing against one locked blade, to cause the other, unlocked, to pivot.
For a two-bladed rotor with blades which can be folded towards the rear, the method may further comprise:
locking the stationary rotor with the first and second blades aligned substantially transversely to a longitudinal axis of the rotary-wing aircraft; and
attaching pivotally the linear actuator to a forward part of one blade and a rearward part of the other blade such that the linear actuator extends rearwardly of a line passing through the pivot axes of the two blades, and such that the linear actuator is disposed rearwardly of the hub of the rotor.
In this way, steps (a) to (d) may be used to bring the first blade from its transversely aligned fixed position to the new position towards the rear of the rotary-wing aircraft, and steps (e) to (f) may be used to bring the second blade 10 from its transversely aligned fixed position to its new position. In this case, the method may in addition comprise the step consisting in attaching the actuator to the blades by means of two securing brackets previously removably attached, one projecting towards the front of the leading edge of the root portion of one blade and the other projecting towards the rear of the trailing edge of the root portion of the other blade.
In the case of a three-bladed rotor with blades which can be folded towards the rear, the method may further comprise:
locking the stationary rotor with the second blade aligned over the rear part of the rotary-wing aircraft;
removable attaching a variable-length linear actuator to the second and third blades;
releasing the third blade from its fixed position;
actuating the linear actuator to vary its length and pivot the third blade about its pivot axis to a new position with respect to the hub; and
locking the third blade in its new position.
In this way, steps (a) to (d) may be used to bring the first blade from its fixed position (unfolded configuration) to the new position towards the rear of the rotary-wing aircraft and adjacent the second blade, and the third blade may be likewise be moved from its fixed position (unfolded configuration) to its new position adjacent the second blade. As a variant, a single actuator may be removably attached firstly to the second blade and to one of the other two blades, to fold or unfold it, then detached and removably attached to the second blade, and to the other of the other two blades, to fold or unfold the latter.
In cases where two actuators are used, the method may advantageously comprise in addition the step consisting in attaching the two actuators substantially to the same attachment point on the rear blade, substantially along the longitudinal axis of said rear blade and radially towards the outside of the pivot axis of said rear blade relative to the axis of rotation of the rotor.
Finally, to fold towards the rear the blades of a rotor with at least four blades, with a third blade and fourth blade each connected to and fixed in position with respect to the hub of the rotor in an analogous way to the first blade, the method further comprises:
locking the stationary rotor with the first and second blades disposed on one side of the rotary-wing aircraft and the third and fourth blades disposed on an opposite side, with the first blade rearwardly of the second blade and the third blade rearwardly of the fourth blade,
carrying out steps (a) to (d) so that the new position of the first blade is over the rear part of the rotary wing aircraft;
repeating steps (a) to (d) for the third blade in place of the first blade so that the third blade is positioned adjacent the first blade;
carrying out steps (e) to (f) for the second blade so that the second blade is positioned adjacent the first blade;
repeating steps (e) to (f) for the fourth blade in place of the second blade so that the fourth blade is positioned adjacent the third blade.
The method may further comprise connecting the first blade to the third blade with a removable link when the first blade is in the new position and the third blade is positioned adjacent to it. As a variant, a single actuator may be used, but it must then be frequently moved to different positions on the rotor in the course of the work.
If the multi-bladed rotor has an odd number of blades, the stationary rotor is locked with one blade positioned over the rear part of the rotary-wing aircraft. In all cases, each blade may be advantageously locked in the folded position by attaching said blade to the rear structure of the rotary-wing aircraft, by means of attachment tools such as folding poles and/or straps and/or supports, as is already known in manual folding.
Regarding the apparatus for folding/unfolding the blades, the removable linear actuator, or each of them, may advantageously comprise at least one double-acting linear jack, comprising at least one rectilinear rod moveable axially in both directions in a jack body, into which said rod is partially inserted and driven by a drive device housed in the body.
The jack may be a fluid-operated jack, i.e. a pneumatic or hydraulic jack, powered either from a pneumatic or hydraulic circuit on board the helicopter, or from the pneumatic or hydraulic outlet of a ground power unit.
However, as this jack is a tool to be installed temporarily on the rotor, it is advantageous for reasons of lightness, bulk and ease of use that this jack should be a simple, lightweight and therefore economical structure, and in particular a mechanical or electromechanical jack, the body of which houses a mechanical drive device with multiplication of force at the rod. In the case of an electromechanical jack, a reduction gear unit driven by an electric motor may be integrated in the jack body and powered from the on-board electrical network of the helicopter or the electrical outlet of a ground electrical generating unit.
Nevertheless, whether the jack drive is mechanical and provided manually or assisted by an electric motor, it is advantageously simple and practical for the mechanical drive device with multiplication of force at the rod to comprise at least one stage of reduction gearing engaged with the rod and using a worm screw, driven in rotation in the body, and/or with gear wheel and pinion gears, said reduction gearing stage comprising at least one input shaft, designed to be driven from the outside of the jack body by mechanical operating means, such as a crank, or electromechanical means, such as a cordless screwdriver, with a battery powered electric motor.
In a simple, economical but nevertheless effective mode of embodiment, the drive device with multiplication of force at the rod comprises a worm gear meshing with the tubular rod into which the worm gear partly extends, and driven in coaxial rotation by an output gear of bevel gearing of which an input opinion is integral with the input shaft, accessible from the outside of the jack body.
Advantageously, to bring together the removable attachment end fittings of the jack and their respective attachment points on the blades, the jack also comprises a manually operated mechanism for disengaging the rod, allowing rapid and simple adjustment of the jack to the desired length, for it to be attached by its end fittings to the attachment devices on two adjacent blades.
Moreover, to reduce loads due to any impacts at the end of the folding or unfolding movement, in particular when an unfolded blade approaches the hub of the rotor or the means of connecting it to this hub, the jack also comprises shock absorbing means, such as at least one axial spring and/or at least one block of elastically deformable material, in series with the rod and/or the body and/or at least one of the end fittings of the jack.
In addition, to avoid the moments induced in the links between the jack and the two blades which it connects by a combination of the pivoting of a folded or unfolded blade and the generally non-zero angle of attack of this blade, the connectors for removably attaching the actuator to the blades comprise at least one ball joint connecting at least one removable attachment end fitting of at least one actuator to at least one corresponding attachment device on a blade, so as to allow the actuator or jack to swivel.
To this end, the ball joint may comprise at least one swivel ball of at least one removable attachment ball joint end fitting of the actuator or jack which cooperates with an attachment pin comprised in said attachment devices fitted to a blade.
However, it is also possible for the ball joint to comprise at least one swivel ball supported by the attachment devices fitted to a blade, so that this swivel ball projects above a portion of root of the blade, and at least one end sleeve of a removable attachment elbow end fitting of an actuator or jack, said sleeve being designed to fit and lock releasably on the swivel ball. This swivel ball may be supported by a support retained by at least one pin or at least one screw in at least one insert of the attachment devices which is integrated in a root portion of the blade, but, as a variant, the swivel ball may be supported by a support integrated directly as an insert in this root portion of the blade.
Generally, the devices attaching an actuator or jack to a blade may be completely integrated in this blade, or comprise at least one attachment element fitted by a removable attachment into at least one other attachment element such as an insert integrated into the root portion of the blade. In both these cases, the blade is not standard, but specific to the folding blade rotor which comprises it.
As a variant, all the devices for attaching an actuator or jack to a blade may be removably fitted to this blade, which is then standard. In a preferred mode of embodiment of attachment means of this type, these attachment means comprise a retaining collar supporting a swivel ball or a pin cooperating with a swivel ball, this retaining collar being removable and designed to grip a part of the root portion of a blade by being locked to the latter by snug fitting and also by a spacer keeping the retaining collar spaced radially towards the outside of the pivot axis of this blade, about which the spacer can pivot with the retaining collar and the blade.